Isoflurane leakage from non-rebreathing rodent anaesthesia circuits: comparison of emissions from conventional and modified ports

Chronic exposure to low levels of fluorocarbon-based waste anaesthetic gas (WAG) has been linked to a multitude of human health problems. We have shown that isoflurane exhaust from passive gas-scavenging canisters is often quite high when using conventional rodent anaesthesia protocols and equipment. Another likely source of WAG build-up in rodent procedure rooms is leakage at the interface between the breathing circuit and the animal's face. We evaluated this possibility using three non-rebreathing circuits: traditional Bain, modified Bain, and Mapleson (type E). For the Mapleson E circuit, a conical rodent facemask was attached and used in one of two configurations: normal aperture, or aperture modified with a latex diaphragm (cut from an unpowdered surgical glove) to reduce the orifice diameter and tighten the seal. Adult female Sprague-Dawley rats were anaesthetized with isoflurane (5% for induction, 2% or 3.5% for maintenance) in oxygen (2 L/min for induction, 1 L/min for maintenance). Isoflurane leakage was assessed by real-time spectrophotometry. In 94% of the trials, three configurations - traditional Bain, modified Bain, and Mapleson E with unmodified mask - permitted isoflurane leakage approaching or exceeding 100 ppm at the face/port interface. In contrast, the Mapleson circuit with diaphragm-modified mask emitted significantly (P